This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
In certain apparatus, the sensitive electronic components/circuitry of a portable electronic apparatus is/are protected by using an exterior protective housing. Such housings provide physical protection against damage, for example from physical forces (e.g. impact) and/or the ingress of liquid. Housings may also/alternatively be used to provide a decorative (user interface) surface for the electronic components/circuitry of the apparatus. Examples of such housings are the so-called A/B/C covers of mobile phones. Although such housings provide the exterior face of the phones, the present invention is not necessarily limited to exterior housings for wireless transmission apparatus, but may be applied to interior housings for wireless transmission apparatus.
The use of metal in housings for mobile phones has been limited due to the inherent nature of metal which can provide a negative shielding effect which would significantly impact the ability of the antenna element to operate effectively at its resonant operating frequency.
Therefore, some forms of metal have been applied to mobile phone housings. For example, metallised paint (e.g. metal flakes in a polymer matrix) has been used to provide the appearance of metal on housings, rather than a true metal housing. Such paints are easily removed by abrasion, particularly at corners. Very thin layers of metal have also been applied using vacuum techniques (e.g. Physical Vapour Deposition (PVD), sputtering, Evaporation Vacuum Metallisation (EVM), Electron Beam-VM (EB-VM)). Again, these metal layers provide very low wear resistance properties, and need to be protected using a transparent protective film. Typically, such applied thin layers are of the order of nanometres or up to (low) tens of micrometres (e.g. 25 microns) or less.
In certain mobile phones, solid (thick) metal covers have been used (e.g. some Vertu™ products). However, regions over the antenna element (in the antenna “significant” radiating direction) have not been covered by metal so that the antenna element may operate effectively. In such regions, plastic/leather, and not metal, has been used over the antenna element areas. Furthermore, in such cases, the metal of/on the housing has been electronically grounded to the ground of the Printed Wiring Board (PWB) of the apparatus.
With regard to the aforementioned “significant radiating direction”, it will be appreciated that antenna elements have front/back radiating faces, and corresponding radiating directions, over which substantially a significant percentage (of the order of 50% or more) of the wireless transmissions are sent/received. It will also be appreciated that the antenna elements have other less significant radiating directions.
U.S. Pat. No. 5,338,617 describes a communications apparatus comprising a receiving antenna, a transmitting antenna and a shield separating said receiving antenna from electromagnetic energy radiated from said transmitting antenna, said shield comprising insulated metal particles, wherein said insulated metal particles include an insulating coating; and a plastic matrix including said insulated metal particles.
U.S. Pat. No. 6,498,292 describes an electrical unit the unit is a mobile telephone comprising two shield parts: a first part and the second part that have a reinforced electrically conductive layer adapted to prevent moisture from reaching the at least one of the first part and the second part, the reinforced electrically conductive layer comprises coarse metal particles in a binder and the binder is selected from the group consisting of acrylic, PVC, and resin.
The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge. One or more aspects/embodiments of the present invention may or may not address one or more of the background issues.